Gasotransmitter H2S accelerates seed germination via activating AOX mediated cyanide-resistant respiration pathway

Hydrogen sulfide (H2S) has been witnessed as a crucial gasotransmitter involving in various physiological processes in plants. H2S signaling has been reported to involve in regulating seed germination, but the underlying mechanism remains poorly understood. Here, we found that endogenous H2S production was activated in germinating Arabidopsis seeds, correlating with upregulated both the transcription and the activity of enzymes (LCD and DES1) responsible for H2S production. Moreover, NaHS (the H2S donor) fumigation significantly accelerated seed germination, while H2S-generation defective (lcd/des1) seeds exhibited decreased germination speed. Further results indicated that the alternative oxidase (AOX), a cyanide-insensitive terminal oxidase, can be stimulated by imbibition, and the expression of AOX genes was provoked lag behind H2S production during germination. Additionally, exogenous H2S fumigation significantly reinforced imbibition induced enhancement of AOX1A expression, and mediated post-translational modification to keep AOX in its reduced and active state, which mainly involved H2S induced increase of the GSH/GSSG ratio and the cell reducing power. Consequently, H2S signaling acts as a trigger to induce AOX mediated cyanide-resistant respiration to accelerate seed germination. Our study correlates H2S signaling to cyanide metabolism, which also participates in endogenous H2S generation, providing evidence for more extensive studies of H2S signaling.

Overexpression of BnaAOX1b Confers Tolerance to Osmotic and Salt Stress in Rapeseed

Alternative oxidases (AOXs) are the terminal oxidase in the cyanide-resistant respiration pathway in plant mitochondria, which play an important role in abiotic stress and are proposed as a functional marker for high tolerant breeding. In this study, ten AOX genes (BnaAOXs) were identified, and CysI and CysII of AOX isoforms were highly conserved in rapeseed. Among them, Bna.AOX1b was mainly expressed in the ovule and displayed varying expression between rapeseed cultivars which showed different salt resistance in seed germination. We identified its mitochondrial localization of this gene. To investigate the function of BnaAOX1b in rapeseed, transgenic rapeseed lines with overexpressed BnaAOX1b were created and seed germination and seedling establishment assays were performed under osmotic, salt, and ABA treatment. The results indicated that overexpression of BnaAOX1b significantly improved seed germination under osmotic and salt stress and weakened ABA sensitivity. In addition, post-germination seedling growth was improved under high salt condition, but showed hypersensitivity to ABA. RNA-sequencing analysis indicated that the genes involved in electron transport or energy pathway were induced and a number of gene responses to salt stress and ABA were regulated in Bna.AOX1b overexpressing seeds. Taken together, our results imply that Bna.AOX1b confers tolerance to osmotic and salt stress in terms of seed germination and seedling establishment by regulating stress responsive genes and the response to ABA, and could be utilized as a candidate gene in transgenic breeding.

Cell Death of Rice Roots under Salt Stress May Be Mediated by Cyanide-Resistant Respiration

Treatment with solutions containing high concentrations of NaCl (200 or 300 mM) induced cell death in rice (Oryza sativa L.) roots, as well as the application of exogenous hydrogen peroxide (H2O2). Moreover, the pretreatment with dimethylthiourea (DMTU), a scavenger of H2O2, partially alleviated the root cell death induced by 200 mM NaCl. These observations suggest that the cell death of rice roots under high salt stress is linked to H2O2 accumulation in vivo. NaCl stress increased the level of cyanide-resistant respiration to some extent and enhanced the transcript levels of the alternative oxidase (AOX) genes AOX1a and AOX1b in rice roots. High-salt-stressed (200 mM NaCl) rice roots pretreated with 1 mM salicylhydroxamic acid (SHAM), a specifi c inhibitor of alternative oxidase, exhibited higher levels of cell death and H2O2 production than roots subjected to either 200 mM NaCl stress or SHAM treatment alone. These results suggest that cyanide-resistant respiration could play a role in mediating root cell death under high salt stress. Furthermore, this function of cyanideresistant respiration could relate to its ability to reduce the generation of H2O2